fixing two bugs in _taggers.py:
fixing two bugs in _taggers.py:

  1)  token might be just part of label_offset.value, even when doing BYTES

  2) if stream_id is not in the XML, then it will be u"" not None

trec-kba/streamcorpus-pipeline,trec-kba/streamcorpus-pipeline,trec-kba/streamcorpus-pipeline